WO2017170329A1

WO2017170329A1 - Multistage compression device, refrigeration cycle comprising same, and operation method for multistage compression device

Info

Publication number: WO2017170329A1
Application number: PCT/JP2017/012258
Authority: WO
Inventors: 政司前野
Original assignee: 三菱重工サーマルシステムズ株式会社
Priority date: 2016-03-28
Filing date: 2017-03-27
Publication date: 2017-10-05
Also published as: JP2017180866A; JP6616224B2; EP3385640A1; EP3385640A4

Abstract

A multistage compression device (20) comprises a plurality of compression groups (20G) arranged in parallel in a circulation line. The compression groups (20G) comprise a plurality of compressors (21) arranged in series, and a series oil equalization line (34) that connects the plurality of compressors (21) to one another. Oil reservoirs (27) of the uppermost stream compressor (21A) of each compression group (20G) are connected to one another by a parallel oil equalization line (39). The end of the uppermost stream compressor (21A), in the parallel oil equalization line (39), which connects with the oil reservoir (27) is open at a position where the oil level is a prescribed level. A rotational frequency setting unit (102) of a control device (100) sets the rotational frequency for each of the plurality of uppermost stream compressors (21A) such that the pressure inside one of the uppermost stream compressors (21A) is less than the pressure inside all of the remaining uppermost stream compressors (21A).

Description

Multistage compressor, refrigeration cycle provided with the same, and operation method of multistage compressor

The present invention relates to a multistage compressor, a refrigeration cycle including the same, and a method for operating the multistage compressor.
This application claims priority based on Japanese Patent Application No. 2016-063568 filed in Japan on March 28, 2016, the contents of which are incorporated herein by reference.

In the refrigeration cycle, a compression device is arranged in a circulation line through which the refrigerant circulates. As this compression apparatus, there is a compression apparatus in which a plurality of compressors are arranged in a circulation line.

As a compression device, for example, there is a device described in Patent Document 1 below. The compressor includes a plurality of low-pressure stage compressors arranged in parallel in a refrigerant circulation line, a high-pressure stage compressor arranged downstream of the plurality of low-pressure stage compressors, and a high-pressure stage compressor And an oil separator disposed on the downstream side. Low pressure discharge lines for each of the plurality of low pressure stage compressors are connected to the discharge ports of the plurality of low pressure stage compressors. The plurality of low pressure discharge lines are connected to a suction port of the high pressure compressor. The plurality of low-pressure discharge lines have different pipe resistances. A high-pressure discharge line is connected to the discharge port of the high-pressure stage compressor. The oil separator described above is provided in the high-pressure discharge line. The low pressure stage compressor to which the discharge line having the largest piping resistance is connected has the highest internal pressure among the plurality of low pressure stage compressors. The low pressure compressor and the oil separator having the highest internal pressure are connected by an oil return line. In addition, the plurality of high-pressure stage compressors are connected by an oil equalizing line.

The oil collected in the oil separator returns to the low pressure stage compressor having the highest internal pressure through the oil return line. Part of the oil that has returned to the low-pressure stage compressor flows into the low-pressure stage compressor having the next highest internal pressure. Part of the oil in the low pressure compressor flows into the low pressure compressor having the next highest internal pressure. Hereinafter, the oil sequentially flows into the low-pressure stage compressor having a low internal pressure. That is, in this multistage compressor, by providing a pipe resistance difference between the low pressure discharge lines connected to each of the plurality of the most downstream low pressure stage compressors, an internal pressure difference is generated between the plurality of low pressure stage compressors. Due to this internal pressure difference, the oil from the oil separator is sequentially sent to a low-pressure compressor having a low internal pressure.

Japanese Patent Application Laid-Open No. 07-301465

In the technique described in Patent Document 1, since it is necessary to provide discharge lines having different pipe resistances for each of the plurality of the most downstream low-pressure compressors, the line configuration becomes complicated and the equipment costs increase. There is. Furthermore, since the piping resistance is purposely provided, the load of each of the plurality of low-pressure stage compressors is increased even during steady operation, which increases the running cost.

Therefore, the present invention provides a multistage compressor capable of adjusting the oil amount of each compressor to a predetermined oil amount while suppressing facility costs and running costs, a refrigeration cycle including the same, and a method for operating the multistage compressor. The purpose is to provide.

A multi-stage compression apparatus as one aspect according to the invention for solving the above problems includes a plurality of compression groups arranged in parallel in a refrigerant circulation line and a parallel oil equalization that connects the plurality of compressor groups to each other. A line and a control device. Each of the plurality of compression groups comprises a plurality of compressors arranged in series and a part of the circulation line so that the refrigerant flows and connects the plurality of compressors. An in-group connection line that is not connected to any compressor that constitutes another compression group, a series oil leveling line that connects the plurality of compressors, and a compression that is provided for each of the plurality of compressors. A rotation speed changer for changing the rotation speed of the machine. The compressor includes a compression section that compresses the refrigerant and changes the rotation speed by the rotation speed changer, and a housing that covers the compression section and stores oil necessary for driving the compression section. The housing is formed with a suction port for sucking the refrigerant, a discharge port for discharging the refrigerant compressed by the compression unit together with the oil, and an oil reservoir for storing the oil. The series oil leveling line has a first end connected to the oil reservoir for every compressor except the most upstream compressor among the plurality of compressors, and a second end is the first end. It is connected to the oil reservoir of the compressor adjacent to the upstream side of the connection source compressor in the same compression group as the connection source compressor. The parallel oil leveling line connects the oil reservoirs in the most upstream compressor for each of the plurality of compression groups. The connection end with the oil reservoir of the most upstream compressor in the parallel oil equalizing line is opened at a position where the amount of oil accumulated in the oil reservoir becomes a predetermined amount between the upper limit value and the lower limit value. . In the case where the control device has oil accumulated up to a level above the opening in the oil reservoir of at least one of the most upstream compressors of the plurality of compression groups. In addition, for each of the plurality of the most upstream compressors, the pressure in the housing of one upstream compressor is lower than the pressure in the housings of all the remaining upstream compressors. And a rotation speed setting section for determining at least one of the rotation speeds of all the remaining most upstream compressors, and the rotation speed setting section for each of a plurality of the most upstream compressors. A rotation speed instruction section for sequentially instructing at least one of the rotation speeds to the corresponding rotation speed changer.

In the multistage compressor, the amount of oil in all the most upstream compressors except for the inside of the most upstream compressor that finally becomes low pressure can be set to a predetermined amount by sequentially lowering the pressure in the plurality of upstream compressors. In addition, the amount of oil in the most upstream compressor at a low pressure can also be set to an oil amount close to a predetermined amount. That is, in the multistage compressor, the oil level in a plurality of the most upstream compressors can be controlled with a simple control and a simple line configuration by arranging the openings of the parallel oil equalizing lines at predetermined positions in the most upstream compressor. It can be adjusted to a predetermined amount.

In the multistage compressor, the plurality of compressors constituting the compression group are connected to each other by a series oil equalizing line, so that the amount of oil equalized among the plurality of compressors constituting the compression group is increased. be able to.

Here, in the multistage compression device, the control device, for every compressor constituting the plurality of compression groups, the operating state of the compressor including the rotation speed of the compressor and the unit time of the oil A storage unit that stores a relationship with the spilled oil amount, and the rotation speed setting unit uses the relationship for each of the plurality of compressors that configure the compression group. The number of rotations of the compressor is determined for each of the plurality of compressors so that the amount of spilled oil of the downstream compressor is smaller than the amount of spilled oil of the upstream compressor of the compressors, and the rotation The number instruction unit may instruct the rotation number changer corresponding to each of a plurality of rotation numbers for each of the plurality of compressors constituting the compression group set by the rotation number setting unit.

In the multistage compressor, each compressor is operated so that the amount of oil spilled from the downstream compressor is smaller than the amount of oil spilled from the upstream compressor. For this reason, in the said multistage compression apparatus, it can prevent that the oil quantity of a downstream compressor becomes a lower limit before the oil quantity of upstream compression becomes a lower limit. In other words, in the multistage compression apparatus, when the oil amount of any compressor becomes the lower limit value, the compressor becomes an upstream compressor. In the oil return operation, the oil diffused in the circulation line returns to the upstream compressor before returning to the downstream compressor. Therefore, in the multistage compressor, even if the oil amount of any compressor reaches the lower limit value, the oil amount of the compressor whose oil amount has reached the lower limit value can be recovered in a short time by the oil return operation. it can.

In any of the above-described multistage compressors, an oil equalizing valve may be provided for each of the plurality of series oil equalizing lines to adjust the flow rate of oil flowing through the series oil equalizing lines.

In the state where the oil reservoir of the downstream compressor and the oil reservoir of the upstream compressor are always in communication through the series oil leveling line, the pressure in the downstream compressor always decreases, and the downstream high pressure In this compressor, the compression efficiency is constantly decreasing. In the multistage compressor, the oil level in the upstream compressor can be recovered by opening the oil equalizing valve only when the need to send the oil accumulated in the downstream compressor into the upstream compressor increases. In addition, the reduction in compression efficiency in the downstream compressor can be made temporary.

In the multistage compression apparatus including the oil equalizing valve, the control device accumulates in the oil reservoir for each of all the compressors other than the most upstream compressor among the plurality of compressors constituting the compression group. An oil amount grasping unit that grasps the amount of the oil that is in the oil sump portion of the target compressor that is one of the compressors among the oil amounts of one or more compressors grasped by the oil amount grasping unit When the oil amount reaches a predetermined upper limit value, the oil amount is provided in the series oil leveling line connecting the oil reservoir of the target compressor and the oil reservoir of the compressor adjacent to the upstream side of the target compressor. An oil leveling valve indicating unit that gives an opening instruction to the target leveling valve.

In the multistage compressor, the oil amount in the upstream compressor can be recovered at an appropriate timing when the oil amount in the upstream compressor is reduced.

In any one of the above multistage compressors, the compressor is provided for each of the plurality of compressors constituting the compression group, and before the refrigerant discharged from the compressor flows into another compressor, the compressor An oil separator that separates the oil from the refrigerant discharged from the oil, and an oil return line that returns the oil separated by the oil separator into the housing of the compressor corresponding to the oil separator; May be provided.

In the multistage compressor, a part of the oil discharged together with the refrigerant from the compressor can be returned to the compressor via the oil separator, so that a decrease in the oil amount of the compressor can be suppressed.

In the multistage compression apparatus including the oil separator, among the oil separators for the plurality of compressors constituting the compression group, the oil separation efficiency of the oil separator with respect to the upstream compressor is lower than the oil separation efficiency of the oil separator. The oil separation efficiency of the oil separator relative to the compressor may be higher.

In the multistage compressor, the oil separation efficiency of the oil separator for the most downstream compressor is higher than the oil separation efficiency of the oil separator for other compressors. For this reason, in the said multistage compression apparatus, the quantity of the oil which flows out into the remaining part in a circulation line from the part into which the refrigerant | coolant of a multistage compression apparatus flows in a circulation line can be suppressed effectively.

In any one of the multistage compressors described above, the control device includes a most upstream oil amount grasping unit that grasps the amount of the oil accumulated in the most upstream compressor for each of a plurality of compression groups, and the most upstream flow. Of the oil amount grasped by the oil amount grasping unit, when the oil amount in at least one uppermost compressor reaches a predetermined lower limit value, for any device connected to the circulation line, An oil return operation instructing unit that instructs the oil in the circulation line to be in a state where it can return to the plurality of the most upstream compressors.

In the multistage compressor, when the oil return operation instruction unit instructs the equipment connected to the circulation line, the oil diffused in the circulation line can be returned to the most upstream compressor.

The refrigeration cycle as one aspect according to the invention for solving the above problems is as follows:
Any one of the multistage compressors described above, and a first heat exchanger that is arranged in the circulation line and causes heat exchange between the refrigerant flowing through the circulation line and the first medium, and phase-changes the refrigerant, A second heat exchanger that is arranged in the circulation line and exchanges heat between the refrigerant flowing through the circulation line and the second medium to change the phase of the refrigerant; the first heat exchanger; and the second heat. Expansion located in the circulation line between the exchangers and in the part of the circulation line where the multistage compressor is not arranged between the first heat exchanger and the second heat exchanger And a valve.

The operation method of the multistage compressor as one aspect according to the invention for solving the above problems is the following operation method of the multistage compressor.
The multistage compressor includes a plurality of compression groups arranged in parallel in the refrigerant circulation line, and a parallel oil equalizing line connecting the plurality of compressor groups. Each of the plurality of compression groups comprises a plurality of compressors arranged in series and a part of the circulation line so that the refrigerant flows and connects the plurality of compressors. An in-group connection line that is not connected to any compressor that constitutes another compression group, a series oil leveling line that connects the plurality of compressors, and a compression that is provided for each of the plurality of compressors. A rotation speed changer for changing the rotation speed of the machine. The plurality of compressors include a compression section that compresses the refrigerant and changes the rotation speed by the rotation speed changer, and a housing that covers the compression section and stores oil necessary for driving the compression section. The housing is formed with a suction port for sucking the refrigerant, a discharge port for discharging the refrigerant compressed by the compression unit together with the oil, and an oil reservoir for storing the oil. The series oil leveling line has a first end connected to the oil reservoir for every compressor except the most upstream compressor among the plurality of compressors, and a second end is the first end. It is connected to the oil reservoir of the compressor adjacent to the upstream side of the connection source compressor in the same compression group as the connection source compressor. The parallel oil leveling line connects the oil reservoirs in the most upstream compressor for each of the plurality of compression groups.
The operation method of the multi-stage compressor is such that the amount of oil accumulated in the oil reservoir is between an upper limit value and a lower limit value at a connection end of the parallel oil leveling line with the oil reservoir of the most upstream compressor. It is opened beforehand at a position where a fixed amount is obtained. Among the most upstream compressors for each of the plurality of compression groups, when oil is accumulated in the oil reservoir of at least one of the most upstream compressors up to a level above the opening, a plurality of the above For each of the most upstream compressors, the rotational speed of the one most upstream compressor and the pressure so that the pressure in the housing of one of the most upstream compressors is lower than the pressure in the housings of all the remaining most upstream compressors. A rotation number setting step for determining at least one rotation number of all the remaining most upstream compressors, and at least one of the plurality of the most upstream compressors determined in the rotation number setting step. And a rotation speed instruction step for sequentially instructing the rotation speed to the corresponding rotation speed changer.

Here, in the operation method of the multistage compressor, the operating state of the compressor including the number of rotations of the compressor and the amount of spilled oil per unit time for all the compressors constituting the plurality of compression groups The plurality of compressions so that the spilled oil amount of the downstream compressor is smaller than the spilled oil amount of the upstream compressor among the plurality of compressors constituting the compression group. The series rotation speed setting step for determining the rotation speed of the compressor for each machine, and the rotation speed corresponding to each of the rotation speeds of the plurality of compressors constituting the compression group determined in the series rotation speed setting step You may perform the serial rotation speed instruction | indication process instruct | indicated to a change device.

Also, in any one of the above-described multistage compressor operation methods, the most upstream oil amount grasping step for grasping the amount of the oil accumulated in a plurality of the most upstream compressors, and the most upstream oil amount grasping step. When the amount of oil in at least one of the most upstream compressors reaches the lower limit determined in advance among the amount of oil grasped in step 1, in any one of the devices connected to the circulation line, An oil return operation instructing step for instructing the oil to return to a state where it can return to the plurality of the most upstream compressors.

In one aspect of the present invention, the amount of oil in each compressor can be adjusted to a predetermined amount while suppressing facility costs and running costs.

It is a systematic diagram of the refrigerating cycle in one embodiment concerning the present invention. It is a systematic diagram of the multistage compressor in one embodiment concerning the present invention. It is a systematic diagram of the compression group in one Embodiment which concerns on this invention. It is a functional block diagram of a control device in one embodiment concerning the present invention. It is explanatory drawing for demonstrating the relationship information in one Embodiment which concerns on this invention. It is a graph which shows the relationship between the superheat degree of an oil sump part, and the amount of discharged oil. It is a flowchart which shows operation | movement of the control apparatus in one Embodiment which concerns on this invention. It is explanatory drawing which shows the oil quantity change in the high pressure stage compressor in one Embodiment which concerns on this invention, and the oil quantity change of a low pressure stage compressor. It is explanatory drawing which shows the state from which the oil quantity of one of the some low pressure stage compressors in one Embodiment which concerns on this invention became a lower limit. It is explanatory drawing which shows the oil quantity change in the some low pressure stage compressor in one Embodiment which concerns on this invention. (A) of FIG. 8 is explanatory drawing which shows the oil quantity in the several low pressure stage compressor immediately after an oil return process. (B) of FIG. 8 is explanatory drawing which shows the oil quantity in a several low pressure stage compressor at the time of making the inside of a 1st low pressure stage compressor into a low pressure. (C) of FIG. 8 is explanatory drawing which shows the oil quantity in a several low pressure stage compressor at the time of making the inside of a 2nd low pressure stage compressor into a low pressure. (D) of FIG. 8 is explanatory drawing which shows the oil quantity in a several low pressure stage compressor at the time of making the inside of a 3rd low pressure stage compressor into a low pressure. It is a systematic diagram of the multistage compression apparatus in the modification of one Embodiment which concerns on this invention.

Hereinafter, embodiments and modifications according to the present invention will be described with reference to the drawings.

"Embodiment"
An embodiment of a refrigeration cycle according to the present invention will be described with reference to FIGS.

As shown in FIG. 1, the refrigeration cycle of the present embodiment includes a first heat exchanger 1, a second heat exchanger 2, an expansion valve 3, a four-way switching valve 4, a circulation line 10, and a multistage compression device. 20 and the control device 100.

The first heat exchanger 1, the second heat exchanger 2, the expansion valve 3, the four-way switching valve 4, and the multistage compression device 20 are all provided in the circulation line 10 through which the refrigerant R flows. The first heat exchanger 1 changes the phase of the refrigerant R by exchanging heat between the refrigerant R and the first medium M1. The second heat exchanger 2 changes the phase of the refrigerant R by exchanging heat between the refrigerant R and the second medium M2. The first heat exchanger 1 has a first refrigerant port 1a and a second refrigerant port 1b. The second heat exchanger 2 also has a first refrigerant port 2a and a second refrigerant port 2b. The multistage compressor 20 compresses the gaseous refrigerant R. The expansion valve 3 reduces the pressure of the liquid refrigerant R. The four-way switching valve 4 has four ports and can selectively change the flow of the refrigerant R between the ports. This four-way switching valve 4 changes the flow of the refrigerant R between the ports by selectively taking the first connection form and the second connection form. In the first connection mode, the first port 4a and the second port 4b are connected, and the third port 4c and the fourth port 4d are connected. The second connection mode is a mode in which the second port 4b and the third port 4c are connected, and the fourth port 4d and the first port 4a are connected.

The circulation line 10 includes a compression line 14 constituting a part of the multistage compressor 20, a first line 11 connected to the first refrigerant port 1 a of the first heat exchanger 1, and the second heat exchanger 2. The second line 12 connected to the first refrigerant port 2a and the third line 13 connected to the second refrigerant port 2b of the second heat exchanger 2 are included. The low pressure side, in other words, the upstream end of the compression line 14 is connected to the third port 4 c of the four-way switching valve 4. The high-pressure side of the compression line 14, in other words, the downstream end is connected to the first port 4 a of the four-way switching valve 4. Of the two ends of the first line 11, one end is connected to the second port 4b of the four-way switching valve 4, and the other end is the first refrigerant port of the first heat exchanger 1 as described above. Connected to 1a. Of the two ends of the second line 12, one end is connected to the second refrigerant port 1b of the first heat exchanger 1, and the other end is the second end of the second heat exchanger 2 as described above. One refrigerant port 2a is connected. Of the two ends of the third line 13, one end is connected to the second refrigerant port 2b of the second heat exchanger 2 as described above, and the other end is the fourth port of the four-way switching valve 4. 4d.

The second refrigerant port 1b of the first heat exchanger 1 and the first refrigerant port 2a of the second heat exchanger 2 are connected by the second line 12 as described above. Further, the second refrigerant port 2 b of the second heat exchanger 2 and the first refrigerant port 1 a of the first heat exchanger 1 are connected by a third line 13, a compression line 14, and a first line 11. The expansion valve 3 is disposed in the second line 12. Therefore, the expansion valve 3 is in the circulation line 10 between the first heat exchanger 1 and the second heat exchanger 2 and between the first heat exchanger 1 and the second heat exchanger 2. It arrange | positions in the circulation line 10 in which the multistage compressor 20 is not arrange | positioned.

As shown in FIG. 2, the multistage compressor 20 includes a plurality of compression groups 20G, a parallel oil equalizing line 39 that connects the plurality of compression groups 20G, and the above-described compression line 14.

Each of the plurality of compression groups 20G includes an accumulator 31, a low-pressure stage compressor 21A, a high-pressure stage compressor 21C, a low-pressure rotation speed changer 29A, a high-pressure rotation speed changer 29C, and a low-pressure oil separator. 32A, a high-pressure oil separator 32C, a part of the above-described compression line 14, a low-pressure oil return line 33A, a high-pressure oil return line 33C, a series oil leveling line 34, and an oil leveling valve 35 are provided. In the present embodiment, the most upstream compressor is the low-pressure stage compressor 21A.

The accumulator 31 has a function of temporarily storing the refrigerant R and separating the liquid-phase refrigerant R and the gas-phase refrigerant R from each other. The accumulator 31 is formed with a refrigerant inlet 31a and a refrigerant outlet 31b.

As shown in FIG. 3, each of the low-pressure stage compressor 21A and the high-pressure stage compressor 21C includes a compression unit 22 that compresses the refrigerant R, a motor 23 that rotates the compression unit 22, and a housing 24 that covers them. Have The compression unit 22 is, for example, a rotary type. The housing 24 has a cylindrical body portion with a central axis extending in the vertical direction as a center, and mirror portions that block openings at both ends of the cylindrical body. A suction port 25 is formed in the body portion of the housing 24, and a discharge port 26 is formed in the mirror portion on the housing 24. The lower part in the housing 24 including the inside of the mirror part below the housing 24 constitutes an oil reservoir part 27 (lower dome part) in which oil O necessary for operating the motor 23 and the compression part 22 is accumulated. The low-pressure rotation speed changer 29A changes the rotation speed of the motor 23 of the low-pressure compressor 21A. The high-pressure rotation speed changer 29C changes the rotation speed of the motor 23 of the high-pressure stage compressor 21C. Each

rotation speed changer

29A, 29C is an inverter which changes the frequency of the alternating current power supplied to the motor 23, for example.

The low pressure oil separator 32A captures a part of the oil O discharged together with the refrigerant R from the low pressure stage compressor 21A. The high pressure oil separator 32C captures a part of the oil O discharged together with the refrigerant R from the high pressure stage compressor 21C. That is, each

oil separator

32A, 32C separates the oil O from the fluid discharged from the

compressors

21A, 21C. The oil separation efficiency of the high pressure oil separator 32C is higher than the oil separation efficiency of the low pressure oil separator 32A.

As a part of the compression line 14, there are a suction line 16, a low pressure discharge line 17, and a high pressure discharge line 18. The suction line 16, the low pressure discharge line 17, and the high pressure discharge line 18 are provided for each of the plurality of compression groups 20G. Of the two ends of the suction line 16, one end is connected to the suction port 25 of the low-pressure compressor 21A. The accumulator 31 is disposed in the suction line 16. Of the two ends of the low-pressure discharge line 17 (intra-group connection line), one end is connected to the discharge port 26 of the low-pressure stage compressor 21A, and the other end is connected to the suction port 25 of the high-pressure stage compressor 21C. It is connected. This low-pressure discharge line 17 is not connected to any compressor 21 constituting another compression group 20G. One of the two ends of the high-pressure discharge line 18 is connected to the discharge port 26 of the high-pressure compressor 21C.

The low pressure oil separator 32 A is disposed in the low pressure discharge line 17. The high pressure oil separator 32 C is disposed in the high pressure discharge line 18. Of the two ends of the low-pressure oil return line 33 A, one end is connected to the low-pressure oil separator 32 A, and the other end is connected to the suction line 16. Of the two ends of the high pressure oil return line 33C, one end is connected to the high pressure oil separator 32C and the other end is connected to the low pressure discharge line 17. Of the two ends of the series oil leveling line 34, one end is connected to the oil reservoir 27 of the high-pressure stage compressor 21C, and the other end is connected to the oil reservoir 27 of the low-pressure stage compressor 21A. Yes. The oil leveling valve 35 is provided in the series oil leveling line 34.

Each of the plurality of compression groups 20G further includes a low pressure thermometer 37A, a high pressure thermometer 37C, a low pressure manometer 38A, and a high pressure manometer 38C. The low-pressure thermometer 37A detects the temperature of the oil O accumulated in the oil reservoir 27 of the low-pressure compressor 21A. The high-pressure thermometer 37C detects the temperature of the oil O accumulated in the oil reservoir 27 of the high-pressure compressor 21C. The low pressure pressure gauge 38A detects the pressure of the refrigerant R sucked by the low pressure compressor 21A, that is, the pressure in the suction line 16. The high pressure gauge 38C detects the pressure of the refrigerant R sucked by the high pressure compressor 21C, that is, the pressure in the low pressure discharge line 17.

As shown in FIG. 3, the compression line 14 constituting a part of the multistage compressor is shared in addition to the suction line 16, the low pressure discharge line 17 and the high pressure discharge line 18 constituting a part of the compression group 20G. A suction line 15 and a common discharge line 19 are provided. One end of the two ends of the common suction line 15 is connected to the third port 4 c of the four-way switching valve 4. The other end of the above-described two ends of the suction line 16 for each of the plurality of compression groups 20G is connected to the other end side of the common suction line 15. Of the two ends of the common discharge line 19, one end is connected to the first port 4 a of the four-way switching valve 4. The other end of the above-described two ends of the high-pressure discharge line 18 for each of the plurality of compression groups 20G is connected to the other end side of the common discharge line 19.

The parallel oil equalization line 39 connects the oil reservoirs 27 in the low-pressure compressor 21A for each of the plurality of compression groups 20G. The connecting end of the parallel oil equalizing line 39 with the oil reservoir 27 is open. The position of the opening 39a is a position where the amount of oil accumulated in the oil reservoir 27 becomes a predetermined amount between the upper limit value Llh and the lower limit value Lll. It is open.

As shown in FIG. 4, the control device 100 includes a receiving unit 101, a rotation number setting unit 102, an oil amount estimation unit 104, an oil amount determination unit 103, a rotation number instruction unit 105, An oil valve instruction unit 106, an expansion valve instruction unit 107, a switching valve instruction unit 108, and a storage unit 109 are included. The control device 100 includes, as a hardware configuration, an arithmetic unit that executes various calculations, a main storage device such as a memory that temporarily stores various programs and various data, and a hard disk drive that stores various programs and various data. An auxiliary storage device such as a device, and an interface circuit for inputting / outputting data to / from the outside. The reception unit 101, the rotation speed instruction unit 105, the oil equalization valve instruction unit 106, the expansion valve instruction unit 107, and the switching valve instruction unit 108 are all stored in the inter base circuit, the main storage device, and the main storage device. And an arithmetic unit that executes the program. The rotation speed setting unit 102, the oil amount estimation unit 104, and the oil amount determination unit 103 are configured to include a main storage device and a calculator that executes a program stored in the main storage device. The storage unit 109 includes a main storage device and an auxiliary storage device.

The accepting unit 101 accepts various information and instructions. The temperature detected by the low-pressure thermometer 37A, the temperature detected by the high-pressure thermometer 37C, the pressure detected by the low-pressure pressure gauge 38A, and the pressure detected by the high-pressure pressure gauge 38C are received by the receiving unit 101. Accept. The rotation speed setting unit 102 sets the rotation speed for each motor 23 of the

compressors

21A and 21C. The oil amount estimation unit 104 estimates the amount of oil accumulated in each oil reservoir 27 of the

compressors

21A and 21C. The oil amount determination unit 103 determines whether or not the oil amount accumulated in the oil reservoirs 27 of the

compressors

21A and 21C has reached the upper limit value or the lower limit value. The rotation speed instruction unit 105 instructs the

rotation speed changers

29A and 29C for the rotation speeds of the

compressors

21A and 21C. The oil equalizing valve instruction unit 106 instructs the oil equalizing valve 35 to open and close. The expansion valve instruction unit 107 instructs the opening degree of the expansion valve 3. The switching valve instruction unit 108 instructs the four-way switching valve 4 as the connection form between the ports as the first connection form or the second connection form.

The storage unit 109 stores information necessary for the rotation speed setting unit 102 to set the rotation speed for each motor 23 of the

compressors

21A and 21C for each of the plurality of compression groups 20G. The information stored in the storage unit 109 includes the initial oil amounts Lls and Lhs of the oil sump 27 in the

compressors

21A and 21C, the oil amounts Llr and Lhr after the oil return operation, and the rotations of the

compressors

21A and 21C. This is the relationship information between the number N and the oil spill amount FO per unit time of the oil O.

The initial oil amounts Lhs and Lls are the amount of oil accumulated in the oil reservoir 27 at the time of product shipment, or the amount of oil immediately after the oil O is replenished from the outside. Further, the oil amounts Lhr and Llr after the oil return operation are the oil amounts accumulated in the oil reservoir 27 immediately after the oil return step described later.

The relationship information between the rotational speed N of the two

compressors

21A and 21C and the amount of spilled oil FO per unit time of the oil O from the

compressors

21A and 21C will be described.

As shown in FIG. 5, the amount of oil O per unit time from the discharge ports 26 of the

compressors

21A and 21C, that is, the amount Q of discharged oil per unit time, increases with an increase in the rotational speed N of the

compressors

21A and 21C. Increase. In FIG. 5, Ql indicates the amount of discharged oil per unit time of the low-pressure stage compressor 21A, and Qh indicates the amount of discharged oil per unit time of the high-pressure stage compressor 21C.

Further, as shown in FIG. 6, the discharged oil amount Q decreases as the superheat degree ΔT of the oil reservoir 27 (lower dome) increases. Therefore, in the present embodiment, as shown in FIG. 5, the discharged oil amount Q corresponding to the rotational speed N is corrected according to the superheat degree ΔT of the oil reservoir 27, and this is set as the corrected discharged oil amount QΔT. . In FIG. 5, Ql _ΔT1 indicates the amount of oil discharged per unit time of the low pressure compressor 21A when the degree of superheat ΔT1, and Ql _ΔT2 indicates the unit time of the low pressure stage compressor 21A when the degree of superheat ΔT2. Indicates the amount of oil discharged per hit. Qh _ΔT1 indicates the amount of oil discharged per unit time of the high pressure compressor 21C when the degree of superheat _ΔT1 , and Qh _ΔT1 indicates the amount of oil discharged per unit time of the high pressure stage compressor 21C when the degree of superheat ΔT2. Indicates the amount.

Here, the superheat degree ΔT of the oil reservoir 27 is a temperature deviation of the temperature Td of the oil reservoir 27 with respect to CSST (Compressor Suction Saturated Temperature) as shown in the following formula (1). is there.
ΔT = Td−CST (1)

In the present embodiment,

oil separators

32A and 32C are provided on the discharge side of the

compressors

21A and 21C. A part of the oil O discharged from the compressor 21 is captured by the oil separator 32. The oil O captured by the oil separator 32 returns from the suction port 25 of the compressor 21 to the oil reservoir 27 of the compressor 21 via the oil return line 33. For this reason, the spilled oil amount FO per unit time from the system including the compressor 21 and the oil separator 32 is captured by the oil separator 32 out of the oil O discharged from the discharge port 26 of the compressor 21. The amount of oil O that did not exist. Therefore, in this embodiment, as shown in the following formula (2), the discharge oil amount Q _ΔT is corrected by the oil separation efficiency a (<1) of the oil separator, and this is calculated as the spilled oil amount FO per unit time. And In FIG. _5, FOl ΔT1a indicates the outflow amount of oil per unit time of the low-pressure compressor 21A when superheat _ΔT1, FOl ΔT2a low-pressure stage unit of the compressor 21A time when the degree of superheat ΔT2 The amount of oil spilled per unit is shown. Further, FOh _ΔT1a indicates the amount of oil spilled per unit time of the high pressure compressor 21C when the degree of superheat ΔT1, and FOh _ΔT2a indicates the spilled oil per unit time of the high pressure stage compressor 21C when the degree of superheat ΔT2. Indicates the amount.
FO = _QΔT × (1-a) (2)

In the present embodiment, the relationship information for each of the plurality of

compressors

21A, 21C includes the spilled oil amount FOl _ΔT1a , FOl _ΔT2a ,..., FOh _ΔT1a , FOh _ΔT2a , ... That is, in this embodiment, for each of the plurality of

compressors

21A and 21C, as shown in the following formula (3), the amount of spilled oil FO per unit time, the rotational speed N of the compressor 21, and the oil reservoir Information on the relationship between the degree of superheat ΔT 27 and the oil separation efficiency a of the oil separator 32 is stored in the storage unit 109.
FO = g (N, ΔT, a) (3)

Among the plurality of parameters constituting the related information, the oil separation efficiency a of the oil separator 32 is a fixed value. Therefore, out of a plurality of parameters constituting the relationship information, the spilled oil amount FO per unit time, the compressor rotation speed N, and the degree of superheat ΔT of the oil reservoir 27 are treated as variables.

The storage unit 109, described above relationship information _{_{FOl ΔT1a, FOlΔ T2a, ...,}} FOh ΔT1a, FOh ΔT2a, ... , is stored in a map form or functional form.

As described above, the control device 100 that is a component of the refrigeration cycle controls each device of the multistage compression device 20. Therefore, the control device 100 is also a component of the multistage compression device 20.

Next, the operation of the refrigeration cycle will be described.

First, the basic operation of the refrigeration cycle when the four-way switching valve 4 is in the first connection configuration will be described. The first connection mode is a mode in which the first port 4a and the second port 4b are connected and the third port 4c and the fourth port 4d are connected as described above.

The gaseous refrigerant R compressed in each compression group 20G of the multistage compressor 20 passes through the first port 4a and the second port 4b of the four-way switching valve 4 and the first line 11 as shown in FIG. It flows into the heat exchanger 1. The gaseous refrigerant R exchanges heat with the first medium M1 in the first heat exchanger 1. As a result, the first medium M1 is heated. On the other hand, the gaseous refrigerant R is cooled and condensed to become a liquid refrigerant R. Therefore, the 1st heat exchanger 1 functions as a condenser, when the four-way switching valve 4 is a 1st connection form.

The refrigerant R liquefied in the first heat exchanger 1 flows into the second heat exchanger 2 through the second line 12. The refrigerant R is decompressed by the expansion valve 3 arranged in the second line 12 in the process of flowing through the second line 12.

The liquid refrigerant R exchanges heat with the second medium M2 in the second heat exchanger 2. As a result, the second medium M2 is cooled. On the other hand, the liquid refrigerant R is heated and vaporized to become a gaseous refrigerant R. Therefore, the 2nd heat exchanger 2 functions as an evaporator, when the four-way switching valve 4 is a 1st connection form.

The refrigerant R vaporized in the second heat exchanger 2 flows into the common suction line 15 of the multistage compressor 20 through the third line 13, the fourth port 4 d and the third port 4 c of the four-way switching valve 4. The gaseous refrigerant R flows through the common suction line 15 and into the suction lines 16 for each of the plurality of compression groups 20G, as shown in FIGS. The refrigerant R flows out into the accumulator 31 in the process of flowing through the suction line 16 and then flows out. In the gaseous refrigerant R, a slight amount of mist liquid refrigerant R may remain. The accumulator 31 separates the liquid refrigerant R from the gaseous refrigerant R and discharges the gaseous refrigerant R.

The gaseous refrigerant R from the accumulator 31 flows into the low pressure stage compressor 21A through the suction line 16 from the suction port 25 of the low pressure stage compressor 21A belonging to the same compression group 20G as the suction line 16. The refrigerant R that has flowed into the low-pressure stage compressor 21A is compressed by the compression unit 22 of the low-pressure stage compressor 21A and then discharged from the discharge port 26 of the low-pressure stage compressor. At this time, part of the oil O in the low-pressure compressor 21 A is also discharged from the discharge port 26.

The refrigerant R and oil O discharged from the low-pressure stage compressor 21A pass through the low-pressure discharge line 17 belonging to the same compression group 20G as the low-pressure stage compressor 21A, and the high-pressure stage compression belonging to the same compression group 20G as the low-pressure stage compressor 21A. It flows into the high-pressure stage compressor 21C from the suction port 25 of the machine 21C. A part of the oil O flows in the low pressure discharge line 17, and the low pressure oil separator 32A provided in the low pressure discharge line 17, that is, the low pressure oil separator belonging to the same compression group 20G as the low pressure stage compressor 21A. Captured at 32A. The oil O captured by the low pressure oil separator 32A returns to the low pressure stage compressor 21A through the low pressure oil return line 33A and the suction line 16.

The refrigerant R flowing into the high-pressure stage compressor 21C is compressed by the compression unit 22 of the high-pressure stage compressor 21C. On the other hand, a part of the oil O flowing into the high pressure stage compressor 21C is accumulated in the oil reservoir 27 in the high pressure stage compressor 21C. The refrigerant R compressed by the compressor 22 is discharged from the discharge port 26 of the high-pressure compressor 21C. At this time, part of the oil O in the high-pressure compressor 21 C is also discharged from the discharge port 26.

The refrigerant R and oil O discharged from the high-pressure compressor 21C flow through the high-pressure discharge line 18 belonging to the same group. A part of the oil O flows in the high-pressure discharge line 18, and the high-pressure oil separator 32C provided in the high-pressure discharge line 18, that is, the high-pressure oil separator belonging to the same compression group 20G as the high-pressure stage compressor 21C. Captured at 32C. The oil O captured by the high pressure oil separator 32C returns to the high pressure stage compressor 21C through the high pressure oil return line 33C and the low pressure discharge line 17.

The refrigerant R and oil O that have passed through the high-pressure oil separator 32C flow into the common discharge line 19 via the high-pressure discharge line 18. The refrigerant R and the oil O from the high-pressure discharge line 18 for each of the plurality of compression groups 20G merge in the common discharge line 19. The refrigerant R and oil O flowing into the common discharge line 19 flows into the first heat exchanger 1 through the first port 4a and the second port 4b of the four-way switching valve 4 and the first line 11.

As described above, the refrigeration cycle of the present embodiment moves the heat of the second medium M2 to the first medium M1 via the refrigerant R when the four-way switching valve 4 is in the first connection form.

Next, the basic operation of the refrigeration cycle when the four-way switching valve 4 is in the second connection mode will be described. As described above, the second connection form is a form in which the second port 4b and the third port 4c are connected, and the fourth port 4d and the first port 4a are connected.

The gaseous refrigerant R compressed in each compression group 20G of the multistage compressor 20 passes through the first port 4a and the fourth port 4d of the four-way switching valve 4 and the third line 13 as shown in FIG. It flows into the heat exchanger 2. The gaseous refrigerant R exchanges heat with the second medium M2 in the second heat exchanger 2. As a result, the second medium M2 is heated. On the other hand, the gaseous refrigerant R is cooled and condensed to become a liquid refrigerant R. Therefore, the second heat exchanger 2 functions as a condenser when the four-way switching valve 4 is in the second connection configuration.

The refrigerant R liquefied by the second heat exchanger 2 flows into the first heat exchanger 1 through the second line 12. The refrigerant R is decompressed by the expansion valve 3 arranged in the second line 12 in the process of flowing through the second line 12.

The liquid refrigerant R exchanges heat with the first medium M1 in the first heat exchanger 1. As a result, the first medium M1 is cooled. On the other hand, the liquid refrigerant R is heated and vaporized to become a gaseous refrigerant R. Thus, the first heat exchanger 1 functions as an evaporator when the four-way switching valve 4 is in the second connection configuration.

The refrigerant R vaporized in the first heat exchanger 1 flows into the common suction line 15 of the multistage compressor 20 through the first line 11, the second port 4 b and the third port 4 c of the four-way switching valve 4. The refrigerant R that has flowed into the common suction line 15 is compressed by the multistage compressor 20 as in the case where the four-way switching valve 4 is in the first connection configuration.

As described above, the refrigeration cycle of the present embodiment moves the heat of the first medium M1 to the second medium M2 via the refrigerant R when the four-way switching valve 4 is in the second connection form.

In the present embodiment, the reception unit 101 receives an instruction to cool or heat the first medium M1, so that the four-way switching valve 4 is in the first connection form or the second connection form.

Next, the detailed operation of the multistage compressor 20 will be described according to the flowchart shown in FIG.

When the reception unit 101 of the control device 100 receives an operation start instruction, each device of the multistage compression device 20 starts to operate. The operation start instruction includes an instruction such as a target temperature of the first refrigerant R in addition to an instruction to cool or heat the first medium M1.

When the receiving unit 101 receives the operation start instruction, the rotation speed setting unit 102 determines the rotation speed setting unit according to the target temperature of the first refrigerant R and the superheat degree ΔT of the compressor 21 included in the operation start instruction. 102 determines the rotational speed of the low-pressure compressor 21A and the rotational speed of the high-pressure compressor 21C for each of the plurality of compression groups 20G (S1: rotational speed setting step (series rotational speed setting step)).

In this rotational speed setting step (S1), the rotational speed setting unit 102 determines the rotational speeds of the

compressors

21A and 21C according to the target temperature of the first refrigerant R and the like. Next, using the information stored in the storage unit 109, the rotation speed setting unit 102 uses the information from the high-pressure stage compressor 21C belonging to the same compression group 20G rather than the spilled oil amount FOL from the low-pressure stage compressor 21A. The rotation speeds of the

compressors

21A and 21C determined according to the target temperature of the first refrigerant R and the like are reset so that the spilled oil amount FOh is reduced.

The rotation speed setting unit 102 first obtains the degree of superheat ΔT of the oil sump 27 of each of the

compressors

21A and 21C. The rotation speed setting unit 102 obtains the degree of superheat ΔT via the receiving unit 101, the temperature detected by the low-pressure thermometer 37A, the temperature detected by the high-pressure thermometer 37C, and the low-pressure pressure gauge 38A. The detected pressure and the pressure detected by the high pressure manometer 38C are acquired.

As explained using Equation (1), the degree of superheat ΔT is a temperature deviation of the temperature Td of the oil reservoir 27 with respect to CSST (Compressor Saturated Temperature). Therefore, the rotation speed setting unit 102 obtains CSST in each of the

compressors

21A and 21C. The CSST is uniformly determined by the pressure of the fluid sucked by the compressor 21. For this reason, the rotation speed setting unit 102 obtains the CSST of the low-pressure stage compressor 21A using the pressure of the refrigerant R sucked by the low-pressure stage compressor 21A detected by the low-pressure pressure gauge 38A. Further, the CSST of the high pressure compressor 21C is obtained using the pressure of the refrigerant R sucked by the high pressure compressor 21C detected by the high pressure gauge 38C. Subsequently, the rotation speed setting unit 102 subtracts the CSST of the low-pressure stage compressor 21A from the temperature of the oil sump part 27 in the low-pressure stage compressor 21A detected by the low-pressure thermometer 37A, and collects in the low-pressure stage compressor 21A. The superheat degree ΔT of the part is obtained. Further, the CSST of the high pressure compressor 21C is subtracted from the temperature of the oil reservoir 27 in the high pressure compressor 21C detected by the high pressure thermometer 37C to obtain the superheat degree ΔT of the reservoir in the high pressure compressor 21C.

Therefore, the superheat degree grasping unit in the present embodiment performs overheating based on the low-pressure thermometer 37A, the high-pressure thermometer 37C, the low-pressure pressure gauge 38A, the high-pressure pressure gauge 38C, and values measured by these measuring instruments. This is constituted by one function of the rotation speed setting unit 102 for obtaining the degree.

When the rotation speed setting unit 102 obtains the degree of superheat ΔT of the oil sump 27 in each of the

compressors

21A and 21C, the rotation speed setting unit 102 uses the relationship information of the low-pressure stage compressor 21A stored in the storage unit 109 to determine the low-pressure stage compressor. The spilled oil amount FOL corresponding to the rotational speed N of 21A and the degree of superheat ΔT is obtained. Specifically, for example, as shown in FIG. 5, when the rotational speed of the low-pressure stage compressor 21A is Nl and the superheat degree of the low-pressure stage compressor 21A is ΔT1, the superheat degree ΔT1 of the low-pressure stage compressor 21A is The spilled oil amount FOl ₍ N1 _{, ΔT1)} corresponding to the rotational speed Nl and superheat degree of the low-pressure compressor 21A corresponding to ΔT1 is obtained using the time relationship information FOl _ΔT1a .

Next, the rotation speed setting unit 102 uses the relationship information of the high-pressure stage compressor 21C stored in the storage unit 109, so that the outflow oil amount Foh of the high-pressure stage compressor 21C is the outflow oil amount of the low-pressure stage compressor 21A. The rotational speed N of the high-pressure stage compressor 21C that is smaller than FOl is determined. Specifically, for example, as shown in FIG. 5, when the spilled oil amount of the low-pressure compressor 21A is FOl _{(Nl, ΔT1)} and the superheat degree of the high-pressure compressor 21C is ΔT2, the rotation speed setting unit First, the spilled oil amount FOh of the high-pressure stage compressor 21C that is smaller by a predetermined amount ΔFO than the spilled oil amount FOl ₍ N1 _{, ΔT1) of the} low-pressure stage compressor 21A is determined. Subsequently, the rotational speed Nh of the high-pressure compressor 21C when the amount of oil spilled from the high-pressure compressor 21C is _FOh is determined using the relationship information FOl _ΔT2a when the superheat degree of the high-pressure compressor 21C is ΔT2.

Thus, the rotational speed N of each of the

compressors

21A and 21C, in which the spilled oil amount FOh from the high-pressure stage compressor 21C is smaller than the spilled oil amount FO1 from the low-pressure stage compressor 21A, is determined. Here, the rotational speed Nh of the high-pressure compressor 21C is determined based on the rotational speed Nl of the low-pressure compressor 21A, but the low-pressure compressor 21A based on the rotational speed Nh of the high-pressure compressor 21C. The number of rotations Nl may be determined.

When the rotation speed setting unit 102 determines the rotation speed N of each

compressor

21A, 21C for each of the plurality of compression groups 20G, the rotation speed instruction unit 105 changes the rotation speed of each

compressor

21A, 21C for each of the plurality of compression groups 20G. The rotation speeds Nl and Nh determined by the rotation speed setting unit 102 are instructed to the

devices

29A and 29C (S2: rotation speed instruction process (series rotation speed instruction process)).

When the rotation speed changer 29 receives an instruction for the rotation speed N from the control device 100, the rotation speed changer 29 sets the rotation speed of the motor 23 of the compressor 21 to the specified rotation speed N. The rotational speeds Nl and Nh of the

compressors

21A and 21C determined by the rotational speed setting unit 102 are rotations in which the spilled oil amount FOh from the high pressure compressor 21C is smaller than the spilled oil amount FOl from the low pressure compressor 21A. Is a number. Therefore, as shown in FIG. 8, the amount of oil in the oil reservoir 27 in the low-pressure stage compressor 21A basically decreases with time, and conversely, the oil reservoir 27 in the high-pressure compressor 21C. The amount of oil increases with time.

Next, the oil amount estimation unit 104 estimates the oil amount of the oil reservoir 27 in the high-pressure compressor 21C for each of the plurality of compression groups 20G (S3: oil amount estimation step of the high-pressure compressor). As described above, the amount of oil in the oil reservoir 27 in the high-pressure compressor 21C increases with time. The amount of increase ΔL per unit time of the oil amount is calculated based on the outflow per unit time of the high-pressure stage compressor 21C from the spilled oil quantity FOL per unit time of the low-pressure stage compressor 21A as shown in the following equation (4). This is a value obtained by subtracting the oil amount FOh.
ΔL = FO1-FOh (4)

Therefore, the oil amount estimation unit 104 obtains the temperature detected by the low-pressure thermometer 37A, the pressure detected by the low-pressure pressure gauge 38A, the rotational speed of the low-pressure compressor 21A, and the relationship information of the low-pressure compressor 21A. The spilled oil amount FOl per unit time of the low-pressure stage compressor 21A is used. Further, the oil amount estimation unit 104 uses the temperature detected by the high pressure thermometer 37C, the pressure detected by the high pressure manometer 38C, the rotation speed of the high pressure compressor 21C, and the relationship information of the high pressure compressor 21C. Thus, the spilled oil amount FOh per unit time of the high-pressure compressor 21C is obtained. Then, by subtracting the spilled oil amount FOh per unit time of the high-pressure stage compressor 21C from the spilled oil amount FOl per unit time of the low-pressure stage compressor 21A, the oil amount per unit time in the high-pressure stage compressor 21C is increased. The amount ΔL is obtained.

Subsequently, the oil amount estimation unit 104 accumulates the amount of increase ΔL in the oil amount per unit time for the time from the start time of the increase in the oil amount of the oil reservoir 27 in the high pressure compressor 21C to the current time. An increase amount ΣΔL of the oil amount from the increase start time of the oil amount of the oil reservoir 27 in the stage compressor 21C to the current time is obtained. Then, the oil amount estimation unit 104 adds the increase amount ΣΔL to the oil amount at the oil amount increase start time, and obtains the oil amount L _h (t) of the oil reservoir 27 in the current high-pressure compressor 21C. presume. Note that the oil amount at the oil amount increase start time is the aforementioned initial oil amount Lhs, the oil amount Lhr immediately after the end of the oil return operation described later, the oil amount immediately after the oil leveling operation described later, and the like.

Next, the oil amount estimation unit 104 estimates the oil amount of the oil reservoir 27 in the low-pressure compressor 21A for each of the plurality of compression groups 20G (S4: oil amount estimation step of the low-pressure compressor 21A). A method for estimating the amount of oil in the oil reservoir 27 in the high-pressure compressor 21C will be described later.

When the oil amount estimation unit 104 estimates the oil amount of the oil reservoir 27 in the low pressure stage compressor 21A for each of the plurality of compression groups 20G, the oil amount determination unit 103 sets the low pressure stage compressor 21A for each of the plurality of compression groups 20G. It is determined whether or not the oil amount Ll has become equal to or less than a predetermined lower limit value Lll (S5: low pressure stage lower limit value determination step). If the oil amount determination unit 103 determines that the oil amount Ll of the low-pressure compressor 21A of any compression group 20G has become equal to or lower than the lower limit value Lll, the oil amount determination unit 103 notifies the rotation number instruction unit 105 and the expansion valve instruction unit 107 accordingly. Then, the oil return processing step (S10) for returning the oil O diffused in the circulation line 10 into the low-pressure stage compressor 21A of each compression group 20G is executed. On the other hand, if the oil amount determination unit 103 determines that the oil amount Ll of the low pressure compressors 21A of all the compression groups 20G is not less than the lower limit Lll, the oil amount of the high pressure compressor 21C for each of the plurality of compression groups 20G. It is determined whether or not Lh has reached a predetermined upper limit value Lha (S6: upper limit value determination step of the high-pressure compressor).

If the oil amount Lh of the high-pressure stage compressor 21C is not the upper limit value Lha, the process returns to the rotation speed setting step (S1). On the other hand, if the oil amount Lh of the high-pressure stage compressor 21C has reached the upper limit value Lha, the oil amount determination unit 103 notifies the oil equalization valve instruction unit 106 to that effect. When the oil equalization valve instruction unit 106 receives this notification from the oil amount determination unit 103, the oil equalization valve instruction unit 106 instructs the oil equalization valve 35 of the same compression group 20G as the high pressure compressor 21C to open only for a predetermined time ( S7: Inline oil leveling step). When the oil leveling valve 35 receives this instruction, it opens for a predetermined time and then closes.

The pressure in the housing 24 of the high pressure stage compressor 21C is higher than the pressure in the housing 24 of the low pressure stage compressor 21A of the same compression group 20G. For this reason, when the oil equalizing valve 35 of the same compression group 20G is opened, the oil O accumulated in the oil sump 27 of the high pressure stage compressor 21C is passed through the series oil equalizing line 34 and the oil equalizing valve 35. It begins to flow into the oil reservoir 27 of the compressor 21A. As a result, as shown in FIG. 8, the amount of oil in the high-pressure stage compressor 21C gradually decreases from the opening time t1 of the oil equalizing valve 35, while the amount of oil in the low-pressure stage compressor 21A gradually increases.

The inflow amount of oil O per unit time into the low-pressure compressor 21A is the difference between the pressure in the housing 24 of the high-pressure compressor 21C and the pressure in the housing 24 of the low-pressure compressor 21A, and the series average. It is determined by the flow path resistance of the oil line 34 and the oil equalizing valve 35. The flow resistance of the series oil leveling line 34 and the oil leveling valve 35 is a fixed value. The pressure difference between the pressure in the housing 24 of the high pressure compressor 21C and the pressure in the housing 24 of the low pressure compressor 21A is also substantially constant. Therefore, in this embodiment, assuming that the inflow amount of oil O per unit time determined according to the pressure difference and the flow resistance is constant, the oil amount actually flowing into the low-pressure compressor 21A is the target oil amount. The time until the amount is reached is determined, and the oil equalizing valve 35 is opened by this time Δt. That is, as shown in FIG. 8, if the oil leveling valve 35 is opened at time t1, the oil leveling valve 35 is closed at time t1a after Δt time from this time t1. The pressure in the housing 24 of the high-pressure stage compressor 21C and the pressure in the housing 24 of the low-pressure stage compressor 21A are detected by pressure gauges, and the oil equalizing valve 35 is opened according to the pressure difference. Time may be set.

As a result, the oil amount of the high-pressure stage compressor 21C is reduced from the upper limit value Lha, for example, less than the initial oil amount Lhs of the high-pressure stage compressor 21C and lower than the lower limit value Lhl of the oil amount of the high-pressure stage compressor 21C. A large amount of oil. The upper limit value Lha here is smaller than the upper limit value Lhh determined from the viewpoint of operation of the high pressure stage compressor 21C, and the oil O in the high pressure stage compressor 21C is put into the low pressure stage compressor 21A. It is an upper limit value as a threshold for sending. On the other hand, the oil amount of the low-pressure stage compressor 21A increases from, for example, an oil amount smaller than the initial oil amount Lls of the low-pressure stage compressor 21A, for example, greater than the initial oil amount Lls of the low-pressure stage compressor 21A. The oil amount is smaller than the upper limit value Llh of the oil amount of the stage compressor 21A.

Thereafter, when the reception unit 101 receives an operation stop instruction (S8), the reception unit 101 notifies the oil leveling valve instruction unit 106 and the rotation speed instruction unit 105 to that effect, and causes them to execute a stop process (S9). : Stop processing). Upon receiving this notification, the oil equalizing valve instructing unit 106 instructs the oil equalizing valves 35 for each of the plurality of compression groups 20G to open for a predetermined time Δt. As a result, all the oil leveling valves 35 are temporarily opened. Subsequently, the rotation speed instruction unit 105 instructs the

rotation speed changers

29A and 29C of the

compressors

21A and 21C for each of the plurality of compression groups 20G to turn the rotation speed 0, that is, stop. As a result, all the

compressors

21A and 21C are stopped.

On the other hand, if the receiving unit 101 does not receive the operation stop instruction (S8), the process returns to the rotation speed setting step (S1). Then, the steps S1 to S8 described above are repeatedly executed. In this process, in the high-pressure compressor 21C, as shown in FIG. 8, the increase in the oil amount and the decrease in the oil amount due to the execution of the series oil equalizing step (S7) are repeated. Further, in the low-pressure stage compressor 21A, the oil amount is repeatedly decreased and the oil amount is increased by executing the series oil equalizing step (S7).

By the way, the oil amount of the high-pressure stage compressor 21C returns to the upper limit value Lha of the high-pressure stage compressor 21C even if the series oil leveling step (S7) is repeatedly executed. On the other hand, regarding the low-pressure stage compressor 21A, the oil amount immediately after the execution of the series oil leveling step (S7) decreases every time the series oil leveling step (S7) is executed. This is because the oil O diffuses from the line system of the multistage compressor 20 into the remaining lines in the circulation line 10 by the amount of oil FOh flowing out from the high pressure compressor 21C. For this reason, even if the oil amount of the low-pressure stage compressor 21A is increased in the series oil leveling step (S7), the oil amount of the low-pressure stage compressor 21A remains after the execution of the series oil leveling step (S7) a plurality of times. The lower limit Lll is reached.

Therefore, in the present embodiment, in the steps S1 to S8 described above, the oil amount estimation step (S4) of the low pressure compressor 21A and the lower limit determination step of the low pressure compressor 21A for each of the plurality of compression groups 20G. (S5) is executed. And in this embodiment, when it determines with the lower limit value determination process (S5) of the low pressure stage compressor 21A, the oil quantity of the low pressure stage compressor 21A in any compression group 20G will be below the lower limit value Lll, An oil return process step (S10) is performed.

As described above, the oil amount per unit time diffused from the line system of the multistage compressor 20 into the remaining lines in the circulation line 10 is the spilled oil amount FOh per unit time from the high pressure compressor 21C. For this reason, as shown in the following formula (5), the total oil amount L _total (t) obtained by combining the oil amount of the low-pressure stage compressor 21A and the oil amount of the high-pressure stage compressor 21C at the present time is close. From the total oil amount (Llr + Lhr), which is the sum of the oil amount Llr of the low pressure stage compressor 21A and the oil amount Lhr of the high pressure stage compressor 21C immediately after the oil return operation, the spilled oil per unit time from the high pressure stage compressor 21C This is a value obtained by subtracting a value ΣFOh obtained by integrating the amount FOh for the time from the oil return operation to the current time.
L _total (t) = (Llr + Lhr) −ΣFOh (5)

Moreover, as shown in the following formula (6), the oil amount L _l (t) of the current low-pressure stage compressor 21A is _calculated from the current _total oil amount L _total (t) to the oil amount of the current high-pressure stage compressor 21C. This is a value obtained by subtracting the amount L _h (t).
L _l (t) = L _total (t) −L _h (t) (6)

Therefore, the oil amount estimation unit 104 calculates the oil amount L _l (t) of the low pressure stage compressor 21A at the current time by executing the above expressions (5) and (6) (S4: low pressure stage compression). Oil amount estimation step of machine 21A). Here, the oil amount estimation unit 104 acquires from the storage unit 109 the oil amount Llr of the low-pressure stage compressor 21A and the oil amount Lhr of the high-pressure stage compressor 21C immediately after the oil return operation in Expression (5). In addition, the oil amount estimation unit 104 calculates the current high pressure stage in the oil amount estimation step (S3) of the high pressure stage compressor 21C as the spilled oil quantity FOh per unit time of the high pressure stage compressor 21C in Expression (5). The spilled oil amount FOh obtained in the process of estimating the oil amount L _h (t) of the compressor 21C is used. Furthermore, the oil amount estimation unit 104 obtains the oil amount L _h (t) of the high-pressure stage compressor 21C at the current time in the equation (6) at the oil amount estimation step (S3) of the high-pressure stage compressor 21C. The oil amount L _h (t) of the high-pressure compressor 21C is used. In this embodiment, since the oil amount estimation unit 104 grasps the oil amount in the most upstream compressor 21A, the oil amount estimation unit 104 constitutes the most upstream oil amount grasping unit.

When the oil amount estimation unit 104 estimates the oil amount of the oil reservoir 27 in the low-pressure stage compressor 21A, as described above, the oil amount determination unit 103 performs the oil amount of the low-pressure stage compressor 21A for each of the plurality of compression groups 20G. It is determined whether or not Ll is equal to or lower than the lower limit value Lll (S5: lower limit value determining step of the low-pressure compressor). When the oil amount determination unit 103 determines that the oil amount Ll of the low pressure stage compressor 21A in all the compression groups 20G is not less than or equal to the lower limit value Lll, as described above, the high pressure stage compression is performed for each of the plurality of compression groups 20G. The upper limit determination process (S6) of the machine 21C is executed. On the other hand, if the oil amount determination unit 103 determines that the oil amount Ll of the low-pressure stage compressor 21A of any one of the compression groups 20G is equal to or lower than the lower limit value Lll, as shown in FIG. 105 and the expansion valve instruction unit 107. When receiving the notification from the oil amount determination unit 103, the rotation number instruction unit 105 corresponds to a rotation number corresponding to a predetermined rotation number for the oil return operation for each of the

compressors

21A and 21C for each of the plurality of compression groups 20G. Instruct the

changers

29A and 29C. As a result, the rotational speeds of the

compressors

21A and 21C become the rotational speeds for oil return operation. Further, when the expansion valve instructing unit 107 receives a notification from the oil amount determining unit 103, the expansion valve instructing unit 107 instructs the expansion valve 3 to set a predetermined valve opening for oil return operation. As a result, the expansion valve 3 has a valve opening for oil return operation (S10: oil return processing step). Therefore, in this embodiment, the rotation speed instruction unit 105 and the expansion valve instruction unit 107 constitute an oil return operation instruction unit.

Here, in order to perform the oil return operation, the rotational speeds of the

compressors

21A and 21C and the valve opening degree of the expansion valve 3 are adjusted. However, there are various known methods for oil return operation. For this reason, in this oil return process step (S10), the oil return operation may be executed by another known method.

When the oil return process, in other words, the oil return operation is executed, the oil O diffused in the circulation line 10 returns to the low-pressure stage compressor 21A for each of the plurality of compression groups 20G, and is shown in FIG. As described above, the oil amount of the low-pressure compressor 21A is larger than the lower limit value Lll of the oil amount of each low-pressure compressor 21A. However, the oil amount of each low-pressure compressor 21A is different from each other. This is because the resistance and the like of the suction line 16 connected to the suction port 25 of the low-pressure compressor 21A and the accumulator 31 arranged in the suction line 16 are different for each of the plurality of compression groups 20G. Here, as a result of the oil return operation, for example, as shown in FIG. 10A, the oil level in the first low-pressure stage compressor 21 Ax is higher than the lower limit value Lll, but the opening 39 a of the parallel oil equalizing line 39. It becomes lower than the position of. It is assumed that the oil level in the second low-pressure stage compressor 21Ay is higher than the lower limit value Lll and further higher than the position of the opening 39a of the parallel oil equalizing line 39. Further, it is assumed that the oil level in the third low-pressure stage compressor 21Az is higher than the lower limit value Lll but lower than the position of the opening 39a of the parallel oil equalizing line 39.

The first low-pressure stage compressor 21Ax is the low-pressure stage compressor 21A belonging to the first compression group 20Gx among the plurality of compression groups 20G. The second low-pressure stage compressor 21Ay is a low-pressure stage compressor 21A belonging to the second compression group 20Gy among the plurality of compression groups 20G. The third low-pressure stage compressor 21Az is a low-pressure stage compressor 21A belonging to the third compression group 20Gz among the plurality of compression groups 20G.

Therefore, in this embodiment, the parallel oil leveling process (S11) is executed after the oil return process (S10).

In the parallel oil equalization amount processing step (S11), first, the rotation speed setting unit 102 sets all the remaining pressures in the first low-pressure stage compressor 21Ax among the low-pressure stage compressors 21A for each of the plurality of compression groups 20G. The rotational speed of at least one of the rotational speed of the first low-pressure stage compressor 21Ax and the rotational speeds of all the remaining low-pressure stage compressors 21A is determined so as to be lower than the pressure in the low-pressure stage compressor 21A. For example, the rotational speed of the first low-pressure stage compressor 21Ax is made relatively higher than the rotational speeds of all the remaining low-pressure stage compressors 21Ay and 21Az. As this method, a method of increasing the rotational speed of the first low-pressure stage compressor 21Ax from the current rotational speed, a method of reducing the rotational speeds of all the remaining low-pressure stage compressors 21Ay and 21Az from the current rotational speed, There is a method in which the rotational speed of one low-pressure stage compressor 21Ax is made higher than the current rotational speed, and the rotational speeds of all the remaining low-pressure stage compressors 21Ay and 21Az are made lower than the current rotational speed.

Similarly, the rotation speed setting unit 102 rotates the rotation speed of the second low-pressure stage compressor 21Ay so that the pressure in the second low-pressure stage compressor 21Ay is lower than the pressure in all the remaining low-pressure stage compressors 21Az and 21Ax. And at least one of the remaining low-pressure compressors 21Az and 21Ax is determined. Further, the rotation speed setting unit 102 determines the rotation speed of the third low-pressure stage compressor 21Az so that the pressure in the third low-pressure stage compressor 21Az is lower than the pressure in all the remaining low-pressure stage compressors 21Ax, 21Ay. The rotational speed of at least one of the remaining low-pressure compressors 21Ax and 21Ay is determined.

As described above, the rotation speed setting unit 102 is configured so that the pressure in one low-pressure stage compressor 21A is lower than the pressure in all the remaining low-pressure stage compressors 21A for every low-pressure stage compressor 21A. The rotational speed of at least one of the rotational speed of one low-pressure compressor 21A and the rotational speeds of all the remaining low-pressure compressors 21A is determined (S12: rotational speed setting step).

Next, the rotation speed instruction unit rotates the rotation speed at which the pressure in the first low-pressure stage compressor 21Ax can be lower than the pressure in all the remaining low-pressure stage compressors 21Ay and 21Az, and in the second low-pressure stage compressor 21Ay. The rotation speed at which the pressure can be lower than the pressure in all the remaining low-pressure stage compressors 21Az and 21Ax, the pressure in the third low-pressure stage compressor 21Az is lower than the pressure in all the remaining low-pressure stage compressors 21Ax and 21Ay The possible rotation number is sequentially instructed to the corresponding rotation changer (S13: rotation number instruction step).

As a result, first, the pressure in the first low-pressure stage compressor 21Ax becomes lower than the pressure in all the remaining low-pressure stage compressors 21Ay and 21Az. As described above with reference to FIG. 10A, as a result of the oil return processing step (S10), the oil level in the second low-pressure stage compressor 21Ay is higher than the lower limit Lll, and further, the parallel oil leveling line 39 When the position becomes higher than the position of the opening 39a, the oil in the second low-pressure stage compressor 21Ay is sucked into the low-pressure first low-pressure stage compressor 21Ax as shown in FIG. For this reason, while the amount of oil in the second low-pressure stage compressor 21Ay decreases, the amount of oil in the first low-pressure stage compressor 21Ax increases. However, when the oil level in the second low-pressure stage compressor 21Ay reaches the position of the opening 39a of the parallel oil leveling line 39 in the second low-pressure stage compressor 21Ay, the oil flows out from the second low-pressure stage compressor 21Ay. Disappear. Further, as described above with reference to (a) of FIG. 10, the oil level in the third low-pressure stage compressor 21 Az is higher than the lower limit value Lll as a result of the oil return processing step (S 10). When the position is lower than the position of the opening 39a of 39, the oil in the third low-pressure stage compressor 21Az is not sucked into the low-pressure first low-pressure stage compressor 21Ax. That is, as shown in FIG. 10 (b), the oil level in the third low-pressure stage compressor 21Az does not change.

Next, the pressure in the second low-pressure stage compressor 21Ay becomes lower than the pressure in all the remaining low-pressure stage compressors 21Az and 21Ax. At this time, as shown in FIG. 10C, the oil in the first low-pressure stage compressor 21Ax is sucked into the low-pressure second low-pressure stage compressor 21Ay. For this reason, the amount of oil in the first low-pressure stage compressor 21Ax decreases, while the amount of oil in the second low-pressure stage compressor 21Ay increases. However, when the oil level in the first low-pressure stage compressor 21Ax reaches the position of the opening 39a of the parallel oil leveling line 39 in the first low-pressure stage compressor 21Ax, the oil flows out from the first low-pressure stage compressor 21Ax. Disappear. Further, although the oil level in the third low-pressure stage compressor 21Az is higher than the lower limit Lll, but lower than the position of the opening 39a of the parallel oil equalizing line 39, the oil in the third low-pressure stage compressor 21Az is low pressure. Is not sucked into the second low-pressure stage compressor 21Ay. That is, the oil level in the third low-pressure stage compressor 21Az does not change as in the case where the pressure in the first low-pressure stage compressor 21Ax becomes low.

Finally, the pressure in the third low-pressure stage compressor 21Az becomes lower than the pressure in all the remaining low-pressure stage compressors 21Ax and 21Ay. At this time, as shown in FIG. 10 (d), the oil in the second low-pressure stage compressor 21Ay is sucked into the low-pressure third low-pressure stage compressor 21Az. For this reason, the amount of oil in the second low-pressure stage compressor 21Ay decreases while the amount of oil in the third low-pressure stage compressor 21Az increases. However, when the oil level in the second low-pressure stage compressor 21Ay reaches the position of the opening 39a of the parallel oil leveling line 39 in the second low-pressure stage compressor 21Ay, the oil flows out from the second low-pressure stage compressor 21Ay. Disappear. Further, since the oil level in the first low-pressure stage compressor 21Ax is the level at the position of the opening 39a of the parallel oil equalizing line 39, the oil in the first low-pressure stage compressor 21Ax is low-pressure third low-pressure stage compression. It is not sucked into the machine 21Az. That is, the oil level in the first low-pressure compressor 21 Ax remains unchanged at the level of the opening 39 a of the parallel oil leveling line 39.

This completes the parallel oil leveling process (S11). As a result of the parallel oil leveling step (S11), the oil level in the first low pressure stage compressor 21Ax and the oil level in the second low pressure stage compressor 21Ay are the level at the position of the opening 39a of the parallel oil leveling line 39. become. The oil level in the third low-pressure stage compressor 21Az is slightly higher than the position of the opening 39a of the parallel oil equalizing line 39 in the example shown in FIG. Therefore, the oil level in the low-pressure stage compressor 21A for each of the plurality of compression groups 20G becomes almost the level at the position of the opening 39a of the parallel oil leveling line 39 by the parallel oil leveling process (S11). In the example shown in FIG. 10 (d), as described above, the oil level in the third low-pressure stage compressor 21Az is slightly higher than the position of the opening 39a of the parallel oil equalizing line 39. Yes. However, the oil level in the third low-pressure stage compressor 21Az is slightly lower than the position of the opening 39a of the parallel oil equalizing line 39 due to the total amount of oil in each low-pressure stage compressor 21A after the oil return processing step (S10). In some cases, the level is too low.

When the oil return processing step (S6) is completed, the process returns to the rotation speed setting step (S1).

As described above, in this embodiment, by arranging the opening 39a of the parallel oil equalizing line 39 at a predetermined position in the low-pressure stage compressor 21A, a plurality of low-pressure stage compressions can be performed with simple control and a simple line configuration. The oil amount in the machine 21A can be adjusted to a predetermined oil amount. For this reason, in this embodiment, the complexity of a line structure can be suppressed and the increase in installation cost can be suppressed. Furthermore, in this embodiment, the increase in running cost accompanying the increase in pipe resistance can also be suppressed.

In the present embodiment, the

compressors

21A and 21C are operated such that the spilled oil amount FOh of the downstream high-pressure stage compressor 21C is smaller than the spilled oil amount FOl of the upstream low-pressure stage compressor 21A. The For this reason, in this embodiment, the oil amount of the downstream high-pressure stage compressor 21C is prevented from reaching the lower limit value Lhl before the oil amount of the upstream low-pressure stage compressor 21A becomes the lower limit value Lll. Can do. In other words, in this embodiment, when the oil amount of any of the

compressors

21A and 21C becomes the lower limit value, the compressor becomes the low-pressure compressor 21A on the upstream side. In the oil return operation, the oil O diffused in the circulation line 10 returns to the low pressure stage compressor 21A before returning to the high pressure stage compressor 21C. Therefore, in this embodiment, even if the oil amount of any of the

compressors

21A and 21C becomes the lower limit value, the oil amount of the compressor 21A whose oil amount has reached the lower limit value is recovered in a short time by the oil return operation. Can be made.

In the present embodiment,

oil separators

32A and 32C and

oil return lines

33A and 33C are provided for each of the plurality of

compressors

21A and 21C. For this reason, in this embodiment, the oil amount reduction | decrease of each

compressor

21A, 21C can be suppressed. Furthermore, in the present embodiment, the oil separation efficiency of the high pressure oil separator 32C for the most downstream high pressure stage compressor 21C is higher than the oil separation efficiency of the low pressure oil separator 32A for the low pressure stage compressor 21A. For this reason, in the present embodiment, the amount of oil O flowing out from the system through which the refrigerant R of the multistage compressor 20 flows can be effectively suppressed.

In this embodiment, the oil reservoir 27 of the high-pressure compressor 21C and the oil reservoir 27 of the low-pressure compressor 21A are connected by a series oil leveling line 34. For this reason, in the present embodiment, the oil O accumulated in the high-pressure stage compressor 21C can be sent into the low-pressure stage compressor 21A via the series oil leveling line 34, and the oil pressure in the low-pressure stage compressor 21A can be increased. Oil amount reduction can be suppressed.

In a state where the oil reservoir 27 of the high-pressure compressor 21C and the oil reservoir 27 of the low-pressure compressor 21A are always in communication with each other through the series oil leveling line 34, the pressure in the high-pressure compressor 21C always decreases. The compression efficiency in the high-pressure compressor 21C is constantly reduced. In the present embodiment, an oil equalizing valve 35 is provided in the series oil equalizing line 34. For this reason, in the present embodiment, the oil equalizing valve 35 is opened to open the low pressure stage compressor only when the necessity of sending the oil O accumulated in the high pressure stage compressor 21C into the low pressure stage compressor 21A increases. The amount of oil in 21A can be recovered, and the reduction in compression efficiency in the high-pressure compressor 21C can be made temporary.

In the present embodiment, the oil O that has diffused in the circulation line 10 can be returned to the most downstream high-pressure compressor 21C by executing the oil return operation.

"Variations"
Various modifications of the embodiment described above will be described.

In the above embodiment, the parallel oil leveling process (S11) is performed after the oil return process (S10). However, in the case where the oil is accumulated in at least one low-pressure stage compressor 21A among the low-pressure stage compressors 21A for each of the plurality of compression groups 20G to a level above the opening 39a of the parallel oil equalizing line 39. If there is, the parallel oil equalization amount processing step (S11) may be executed even after the oil return processing step (S10).

In the above embodiment, each low pressure stage compression for reducing the low pressure stage compressor 21A to a low pressure for each of the plurality of low pressure stage compressors 21A in the rotation speed setting step (S12) of the parallel oil leveling process step (S11). After obtaining all the rotation speeds of the machine 21A, the rotation speed instruction step (S13) is executed. However, every time the rotational speed of each low-pressure stage compressor 21A for reducing the pressure of one low-pressure stage compressor 21A among the plurality of low-pressure stage compressors 21A is determined in the rotational speed setting step (S12), the rotational speed You may perform an instruction | indication process (S13).

The level of each opening 39a of the parallel oil equalizing line 39 in the plurality of low-pressure stage compressors 21A does not have to be the same level among the plurality of low-pressure stage compressors 21A. That is, the predetermined value regarding the oil amount in each low-pressure stage compressor 21A may be a predetermined value with respect to the low-pressure stage compressor 21A, and may be different among the plurality of low-pressure stage compressors 21A.

One compression group 20G in the above embodiment is an example in which two

compressors

21A and 21C are arranged in series. However, in the compression group 20G, three or more compressors may be arranged in series. For example, as shown in FIG. 11, three

compressors

21A, 21B, and 21C may be arranged in series. Even in this case, by determining the rotation speed of each compressor so that the spilled oil amount of the downstream compressor is smaller than the spilled oil amount of the upstream compressor, the oil amount is the same as in the above embodiment. Can be recovered in a short time. In this case, the rotation speed setting unit 102 makes the spilled oil amount FLm of the intermediate pressure stage compressor 21B disposed downstream thereof smaller than the spilled oil amount FOl of the most upstream low pressure stage compressor 21A. The rotational speeds of the low-pressure stage compressor 21A and the intermediate-pressure stage compressor 21B are determined. Further, the rotation speed setting unit 102 compresses the high pressure stage so that the spilled oil amount FLh of the high pressure stage compressor 21C disposed on the downstream side is smaller than the spilled oil amount FLm of the intermediate pressure stage compressor 21B. The rotational speed of the machine 21C is determined. In this case as well, the rotational speed of the high-pressure stage compressor 21C may be determined, the rotational speed of the intermediate-pressure stage compressor 21B may be determined, and finally the rotational speed of the low-pressure stage compressor 21A may be determined.

Even when three or more compressors are arranged in series, an oil separator is provided on the downstream side of each compressor, and each oil separator and the corresponding compressor are connected by an oil return line. Is preferred. Also in this case, it is preferable to make the oil separation efficiency of the oil separator with respect to the downstream compressor higher than the oil separation efficiency of the oil separator with respect to the upstream compressor. For example, as shown in FIG. 11, when three

compressors

21A, 21B, and 21C are arranged in series, a low-pressure oil separator 32A is provided on the downstream side of the low-pressure compressor 21A, and this low-pressure oil separator 32A and the low-pressure compressor 21A are connected by a low-pressure oil return line 33A. An intermediate pressure oil separator 32B is provided downstream of the intermediate pressure stage compressor 21B, and the intermediate pressure oil separator 32B and the intermediate pressure stage compressor 21B are connected by an intermediate pressure oil return line 33B. Further, a high pressure oil separator 32C is provided downstream of the high pressure stage compressor 21C, and the high pressure oil separator 32C and the high pressure stage compressor 21C are connected by a high pressure oil return line 33C. Also in the example shown in FIG. 11, the oil separation efficiency of the downstream intermediate pressure oil separator 32B is made higher than the oil separation efficiency of the upstream low pressure oil separator 32A. It is preferable to make the oil separation efficiency of the high-pressure oil separator 32C on the downstream side higher than the oil separation efficiency.

The multistage compression device 20 of the above embodiment includes three compression groups 20G. However, the multistage compression apparatus may include two compression groups 20G or four or more compression groups.

In the above embodiment, the oil amount estimation unit 104 is illustrated as an oil amount grasping unit that grasps the amount of oil accumulated in the compressor 21. However, the oil amount grasping unit may be a liquid meter or a liquid level meter that detects the amount of oil accumulated in the compressor 21.

In the above embodiment, the oil equalizing valve 35 is provided in the series oil equalizing line 34. However, the oil equalizing valve 35 is not necessarily provided in the series oil equalizing line 34. However, when the oil equalizing valve 35 is not provided, as described above, the compression efficiency of the high-pressure compressor 21C is constantly reduced. For this reason, when it is desired to suppress a decrease in the compression efficiency of the high-pressure stage compressor 21C, it is preferable to provide the oil equalizing valve 35 in the series oil equalizing line 34 as in the present embodiment.

In the above embodiment, the oil amount estimating step (S3) of the high pressure stage compressor 21C is executed before the oil amount estimating step (S4) of the low pressure stage compressor 21A. However, after the rotation speed instruction step (S2) and before the upper limit determination step (S6) of the high pressure stage compressor 21C, at what timing the oil amount estimation step (S3) of the high pressure stage compressor 21C is performed. You may go.

The refrigeration cycle in the above embodiment includes a four-way switching valve 4. As described above, the four-way switching valve 4 is provided to switch between the case where the first heat exchanger 1 functions as a condenser and the case where the first heat exchanger 1 functions as an evaporator. . For this reason, when making the 1st heat exchanger 1 function exclusively as a condenser, or when making this 1st heat exchanger 1 function exclusively as an evaporator, the four-way switching valve 4 is unnecessary.

According to one aspect of the present invention, the amount of oil in each compressor can be adjusted to a predetermined amount while suppressing facility costs and running costs.

1: First heat exchanger 2: Second heat exchanger 3: Expansion valve 4: Four-way switching valve 10: Circulation line 11: First line 12: Second line 13: Third line 14: Compression line 15: Shared suction Line 16: Suction line 17: Low pressure discharge line (intra-group connection line)
18: High pressure discharge line 19: Shared discharge line 20: Multistage compressor 20G: Compression group 20Gx: First compression group 20Gy: Second compression group 20Gz: Third compression group 21: Compressor 21A: Low pressure stage compressor (upstream) Compressor)
21Ax: first low-pressure stage compressor 21Ay: second low-pressure stage compressor 21Az: third low-pressure stage compressor 21B: intermediate-pressure stage compressor 21C: high-pressure stage compressor 22: compression unit 23: motor 24: housing 25: suction Port 26: Discharge port 27: Oil reservoir 29: Rotation speed changer 29A: Low pressure rotation speed changer 29C: High pressure rotation speed changer 31: Accumulator 32: Oil separator 32A: Low pressure oil separator 32B: Medium pressure Oil separator 32C: High pressure oil separator 33: Oil return line 33A: Low pressure oil return line 33B: Medium pressure oil return line 33C: High pressure oil return line 34: Series oil equalization line 35: Oil equalization valve 37A: Low pressure thermometer 37C: High pressure thermometer 38A: Low pressure manometer 38C: High pressure manometer 39: Parallel oil leveling line 100: Controller 101: Reception unit 102: Revolution setting unit 103: Oil amount determination unit 104: Oil amount estimation 105: rotational speed instructing section 106: Hitoshiaburaben instruction section 107: expansion valve instructing unit 108: switching valve instructing unit 109: storage unit

Claims

A plurality of compression groups arranged in parallel in the refrigerant circulation line;
A parallel oil equalizing line connecting a plurality of compressor groups;
A control device;
With
Each of the plurality of compression groups comprises a plurality of compressors arranged in series and a part of the circulation line so that the refrigerant flows and connects the plurality of compressors. An in-group connection line that is not connected to any compressor that constitutes another compression group, a series oil leveling line that connects the plurality of compressors, and a compression that is provided for each of the plurality of compressors. A rotation speed changer for changing the rotation speed of the machine,
The compressor has a compression section that compresses the refrigerant and changes the rotation speed by the rotation speed changer, and a housing that covers the compression section and stores oil necessary for driving the compression section,
The housing is formed with a suction port for sucking the refrigerant, a discharge port for discharging the refrigerant compressed by the compression unit together with the oil, and an oil reservoir for storing the oil,
The series oil leveling line has a first end connected to the oil reservoir for every compressor except the most upstream compressor among the plurality of compressors, and a second end is the first end. In the same compression group as the connection source compressor, connected to the oil reservoir of the compressor adjacent to the upstream side of the connection source compressor,
The parallel oil leveling line connects the oil reservoirs in the most upstream compressor for each of the plurality of compression groups,
The connection end with the oil reservoir of the most upstream compressor in the parallel oil leveling line is opened at a position where the amount of oil accumulated in the oil reservoir becomes a predetermined amount between an upper limit value and a lower limit value. ,
The controller is
Among the most upstream compressors for each of the plurality of compression groups, when oil is accumulated in the oil reservoir of at least one of the most upstream compressors up to a level above the opening, a plurality of the above For each of the most upstream compressors, the rotational speed of the one most upstream compressor and the pressure so that the pressure in the housing of one of the most upstream compressors is lower than the pressure in the housings of all the remaining most upstream compressors. A rotation speed setting unit that determines at least one of the rotation speeds of all the remaining upstream compressors;
A rotation speed instruction section that sequentially instructs the rotation speed changer corresponding to the at least one rotation speed determined by the rotation speed setting section for each of a plurality of the most upstream compressors;
Multistage compressor.
The multistage compressor according to claim 1, wherein
The controller is
For each of the compressors constituting the plurality of compression groups, a storage unit that stores the relationship between the operating state of the compressor including the rotation speed of the compressor and the amount of oil spilled per unit time of the oil Have
The rotation speed setting unit uses the relationship for each of the plurality of compressors constituting the compression group, and determines the amount of oil spilled from the upstream compressor among the plurality of compressors constituting the compression group. On the other hand, the rotational speed of the compressor is determined for each of the plurality of compressors so that the amount of oil spilled from the downstream compressor is reduced,
The rotation speed instruction unit instructs the rotation speed changer corresponding to each of the rotation speeds of the plurality of compressors constituting the compression group set by the rotation speed setting unit.
Multistage compressor.
In the multistage compression device according to claim 1 or 2,
Provided for each of the plurality of series oil equalizing lines, and equipped with an oil equalizing valve for adjusting the flow rate of oil flowing through the series oil equalizing line,
Multistage compressor.
In the multistage compression device according to claim 3,
The controller is
Among the plurality of compressors constituting the compression group, an oil amount grasping unit for grasping the amount of the oil accumulated in the oil sump for every compressor except the most upstream compressor;
When the oil amount in the oil reservoir of the target compressor, which is one of the compressors among the oil amounts of one or more compressors grasped by the oil amount grasping unit, reaches a predetermined upper limit value, the target compression An oil leveling valve that gives an opening instruction to a target oil leveling valve provided in the series oil leveling line that connects an oil sump part of a compressor and an oil sump part of a compressor adjacent to the upstream side of the target compressor An indicator,
Having
Multistage compressor.
In the multistage compression device according to any one of claims 1 to 4,
Provided for each of the plurality of compressors constituting the compression group, before the refrigerant discharged from the compressor flows into another compressor, the oil is discharged from the refrigerant discharged from the compressor. An oil separator to separate;
An oil return line for returning the oil separated by the oil separator into the housing of the compressor corresponding to the oil separator;
A multistage compression apparatus.
In the multistage compression device according to claim 5,
Of the oil separators for each of the plurality of compressors constituting the compression group, the oil separation efficiency of the oil separator for the downstream compressor is higher than the oil separation efficiency of the oil separator for the upstream compressor. Is high,
Multistage compressor.
In the multistage compression device according to any one of claims 1 to 6,
The controller is
A most upstream oil amount grasping unit for grasping each amount of the oil accumulated in the most upstream compressor for each of a plurality of compression groups;
When the amount of oil in at least one of the most upstream compressors reaches the lower limit determined in advance among the amount of oil grasped by the most upstream oil amount grasping unit, any device connected to the circulation line On the other hand, an oil return operation instructing unit that instructs the oil in the circulation line to be in a state where it can return to the plurality of the most upstream compressors.
Multistage compressor.
A multistage compression device according to any one of claims 1 to 7;
A first heat exchanger that is disposed in the circulation line and causes heat exchange between the refrigerant flowing through the circulation line and the first medium to change the phase of the refrigerant;
A second heat exchanger that is arranged in the circulation line and exchanges heat between the refrigerant flowing through the circulation line and the second medium to change the phase of the refrigerant;
In the circulation line between the first heat exchanger and the second heat exchanger, the multistage compression device is not disposed between the first heat exchanger and the second heat exchanger An expansion valve arranged in a part in the circulation line;
A refrigeration cycle comprising.
A plurality of compression groups arranged in parallel in the refrigerant circulation line;
A parallel oil equalizing line connecting a plurality of compressor groups;
With
Each of the plurality of compression groups comprises a plurality of compressors arranged in series and a part of the circulation line so that the refrigerant flows and connects the plurality of compressors. An in-group connection line that is not connected to any compressor that constitutes another compression group, a series oil leveling line that connects the plurality of compressors, and a compression that is provided for each of the plurality of compressors. A rotation speed changer for changing the rotation speed of the machine,
The plurality of compressors include a compression section that compresses the refrigerant and changes the rotation speed by the rotation speed changer, and a housing that covers the compression section and stores oil necessary for driving the compression section. ,
The housing is formed with a suction port for sucking the refrigerant, a discharge port for discharging the refrigerant compressed by the compression unit together with the oil, and an oil reservoir for storing the oil,
The series oil leveling line has a first end connected to the oil reservoir for every compressor except the most upstream compressor among the plurality of compressors, and a second end is the first end. In the same compression group as the connection source compressor, connected to the oil reservoir of the compressor adjacent to the upstream side of the connection source compressor,
In the operation method of the multistage compressor, the parallel oil leveling line connects the oil reservoirs in the most upstream compressor for each of the plurality of compression groups.
The connection end of the parallel oil leveling line with the oil reservoir of the most upstream compressor is previously opened at a position where the amount of oil accumulated in the oil reservoir becomes a predetermined amount between the upper limit value and the lower limit value. And
Among the most upstream compressors for each of the plurality of compression groups, when oil is accumulated in the oil reservoir of at least one of the most upstream compressors up to a level above the opening, a plurality of the above For each of the most upstream compressors, the rotational speed of the one most upstream compressor and the pressure so that the pressure in the housing of one of the most upstream compressors is lower than the pressure in the housings of all the remaining most upstream compressors. A rotational speed setting step for determining the rotational speed of at least one of the remaining rotational speeds of the most upstream compressors;
A rotation speed instruction step for sequentially instructing the corresponding rotation speed changer to at least one rotation speed determined in the rotation speed setting step for each of a plurality of the most upstream compressors;
The operation method of the multistage compressor which performs.
In the operation method of the multistage compression device according to claim 9,
The compression group is configured using the relationship between the operating state of the compressor including the number of rotations of the compressor and the amount of oil spilled per unit time for all the compressors constituting the plurality of compression groups. Series rotation that determines the rotation speed of the compressor for each of the plurality of compressors so that the amount of oil spilled by the downstream compressor is smaller than the amount of oil spilled by the upstream compressor among the plurality of compressors Number setting process,
A series rotation speed instruction step for instructing the rotation speed changer corresponding to each rotation speed of each of the plurality of compressors constituting the compression group determined in the series rotation speed setting step;
The operation method of the multistage compressor which performs.
In the operation method of the multistage compressor according to claim 9 or 10,
A most upstream oil amount grasping step for grasping the amount of the oil accumulated in a plurality of the most upstream compressors;
When the amount of oil in at least one of the most upstream compressors reaches the lower limit determined in advance in the amount of oil grasped in the most upstream oil amount grasping step, any device connected to the circulation line On the other hand, an oil return operation instruction step for instructing the oil in the circulation line to be in a state where the oil can return to the plurality of the most upstream compressors;
The operation method of the multistage compressor which performs.